Opinions please. I think it's interference

I would be grateful for your opinions, as I am getting an indication that Plusnet is trying to say my line won't support the speed I know it can.

About 8 weeks ago, just as I changed from Sky to Plusnet, I started to notice that my sync speed, which has been rock solid for 4 years at 17 Mpbs was running much slower. I contacted my then provider and they came out and said there were no faults on the line. I noticed from using a router logger that there were some large changes to the SNR margin on the line at particular times of the day.

I think that this is all being caused by interference from a neighbour. I have attached a graph from tonight that shows the SNR margin at 14db with a sync speed of 8.4 Mbps. My neighbour returns and the SNR plummets. It then resynced to 6db SNR Margin and a sync speed of 5.4 Mpbs. When my neighbour goes to bed I reset the router and it is now stable at 6db SNR margin and 14 Mpbs which is the minimum guaranteed line speed and am more than happy with that speed.

Would you guys who are much more expert than suggest that this is probably due to interference?

If there is anything else you need to know then I will do my best to give you the answer. I just don't want to be fobbed off with 'that's all your line can support' when I know that this is not the case.

Re: Opinions please. I think it's interference

From taking a look at your account, I can see we've sent the fault report back to our suppliers to further investigate and it's been accepted by Openreach which usually means they've identified a potential issue.

Once we have more info, our faults team will follow up via the ticket on your account.